This invention relates to azeotrope-like or constant-boiling mixtures of trifluoromethane and carbon dioxide or trifluromethane, hexafluoroethane and carbon dioxide. These mixtures are useful as refrigerants for heating and cooling and also as fire extinguishing compositions.
Fluorocarbon based fluids have found widespread use in industry for refrigeration applications such as air conditioning and heat pump applications. Vapor compression is one form of refrigeration. In its simplest form, vapor compression involves changing the refrigerant from the liquid to the vapor phase through heat absorption at a low pressure and then from the vapor to the liquid phase through heat removal at an elevated pressure.
While the primary purpose of refrigeration is to remove energy at low temperature, the primary purpose of a heat pump is to add energy at higher temperature. Heat pumps are considered reverse cycle systems because for heating, the operation of the condenser is interchanged with that of the refrigeration evaporator.
Certain chlorofluoromethane and chlorofluoroethane derivatives have gained widespread use as refrigerants in applications including air conditioning and heat pump applications owing to their unique combination of chemical and physical properties. The majority of refrigerants utilized in vapor compression systems are either single components fluids or azeotropic mixtures.
Azeotropic or azeotrope-like compositions are desired as refrigerants because they do not fractionate upon boiling. This behavior is desirable because in the previously described vapor compression equipment with which these refrigerants are employed, condensed material is generated in preparation for cooling or for heating purposes. Unless the refrigerant composition exhibits a constant boiling point, i.e. is azeotrope-like, fractionation and segregation will occur upon evaporation and condensation and undesirable refrigerant distribution may act to upset the cooling or heating.
The art is continually seeking new fluorocarbon and hydrofluorocarbon based azeotrope-like mixtures which offer alternatives for refrigeration and heat pump applications. Fluorocarbon and hydrofluorocarbon based azeotrope-like mixtures are of particular interest because they are considered to be environmentally safe substitutes for the presently used fully halogenated chlorofluorocarbons (CFC's) which are suspected of causing environmental problems in connection with the earth's protective ozone layer. R-503 is an azeotropic blend which consists of trifluoromethane (HFC-23) and chlorotrifluoromethane (CFC-13), a fully halogenated chlorofluorocarbon (U.S. Pat. Nos. 2,101,993 and 2,641,579).
Substitute refrigerants must also possess those properties unique to the CFC's refrigerants including similar refrigeration characteristics, chemical stability, low toxicity, non-flammability, and efficiency in-use. The latter characteristic is important in refrigeration and air-conditioning especially where a loss in refrigerant thermodynamic performance or energy efficiency may have secondary environmental impacts through increased fossil fuel usage arising from an increased demand for electrical energy. Furthermore, the ideal CFC refrigerant substitute would not require major engineering changes to conventional vapor compression technology currently used with CFC refrigerants. Mathematical models have substantiated that hydrofluorocarbons, such as trifluoromethane (HFC-23), will not adversely affect atmospheric chemistry, being a negligible contributor to ozone depletion and to green-house global warming in comparison to the fully halogenated species. HFC-23 alone is not useful as a refrigerant because of a reduction in low evaporator temperature capability.
JO-3,255,189-A published Nov. 14, 1991 teaches a refrigerant composition of HFC-23 and n-pentane.
Bromofluoromethane and bromochlorofluoromethane derivatives, particularly bromotrifluoromethane (Halon 1301) and bromochlorodifluoromethane (Halon 1211) have gained widespread use as fire extinguishing agents in enclosed areas such as airplane cabins and computer rooms. However, the use of these materials is being phased out due to their high ozone depletion. Moreover, as Halons are frequently used in areas where humans are present, suitable replacements must also be safe to humans at concentrations necessary to suppress or extinguish fire.
Low or non-ozone depleting hydrochlorofluorocarbons have been disclosed to be suitable replacements for various Halons in fire extinguishing. For example, U.S. Pat. No. 5,040,609 discloses a process for preventing and controlling fires using a composition containing trifluoromethane. CO.sub.2 is a common fire extinguishing agent used in household fire extinguishers. However, there remains a need for suitable Halon replacements.